1. Field of the Invention
The compositions of the present invention are useful as oxidation inhibitors acting as oxygen-acceptors, peroxide decomposers and electron transfer agents in anti-oxidant processes.
2. Description of the Art
Phenothiazine compounds are known in lubricant products from the U.S. Pat. No. 2,781,318 issued Feb. 12, 1957 to Cyphers. The alkyl phenothiazines of Cyphers are alkylated on the phenylene rings of the phenothiazine structure. Cyphers does not show or suggest the alkylation of the amine nitrogen in phenothiazine. The Cyphers patent is directed to the utility of phenothiazine as an antioxidant and corrosion inhibiting additive for ester, polyester, polyether and other synthetic lubricants.
U.S. Pat. No. 3,536,706 issued Oct. 27, 1970 to Randell suggests that phenothiazines may be used as additives for synthetic lubricants. The phenothiazines particularly described by Randell are those containing tertiary alkyl substituents having from 4 to 12 carbon atoms on the aryl groups which make up the phenothiazine structure. Randell also discloses fused rings on the two phenylene groups which make up the phenothiazine structure. Stated otherwise, Randell allows the utilization of naphthalene for at least one of the two aryl groups in the phenothiazine structure.
U.S. Pat. 3,803,140 issued to Cook et al on Apr. 9, 1974 describes various tertiary alkyl derivatives of phenothiazine. N-alkyl substitution or N-alkenyl substitution is described on the phenothiazine structure. Ring alkylation when the phenothiazine is in the free nitrogen form is also shown. Cook et al express a preference for non-N substituted phenothiazine derivatives.
Cook et al also suggest that organic materials which are susceptible to oxidative degradation may benefit through the use of the compounds of their invention. Such uses include antioxidants for aliphatic hydrocarbons such as gasoline, lubricating oils, lubricating greases, mineral oils, waxes, natural and synthetic polymers such as rubber, vinyl, vinylidene, ethers, esters, amides and urethanes. The compounds of Cook et al are also suggested for stabilizing aldehydes, and unsaturated fatty acids or esters thereof. Still further utilities suggested by Cook et al include the stabilization of organo-metalloid substances such as silicone polymers. Another class of uses of the compounds of Cook et al include the stabilization of vitamins, essential oils, ketones and ethers.
Normant in U.S. Pat. No. 3,560,531 issued Feb. 2, 1971, describes metallation of materials having active hydrogens including phenothiazine. U.S. Pat. No. 3,344,068 issued Sep. 26, 1967, to Waight et al describes antioxidants for ester-based lubricants. Waight et al's compounds have an N-hydrocarbyl substituted phenothiazine structure. The N-substituted phenothiazine compounds of Waight et al are also substituted in at least one position on the fused aromatic nuclei. A second required component in the compositions of Waight et al is a secondary aromatic amine having two aromatic groups attached to the nitrogen atom.
The preparation of alkylthioalkanols which are useful as intermediates for preparing the compounds of the present invention are described in U.S. Pat. No. 4,031,023 to Musser et al. The Musser et al patent was issued Jun. 21, 1977 and is assigned to The Lubrizol Corporation.
U.S. Pat. No. 2,194,527 to Winthrop et al which issued Nov. 24, 1959, describes pharmaceutical compounds such as omega-(10-phenothiazinyl)alkyl di-alkyl sulfonium salts which are useful as spasmolytics and in particular antihistaminics. U.S. Pat. No. 3,376,224 issued April 2, 1968 to Elliott et al describes phenothiazine derivatives which are stated to be N-substituted methylene compounds which contain an ether linkage between the methylene group and an alkyl or cycloalkyl radical. According to Elliot et al, the alkyl or cycloalkyl radical may carry an alkoxy or other non-reactive substituent.
It has been found in the present invention that the antioxidant activity of a phenothiazine is significantly improved by the presence of a sulfur-containing hydrocarbyl moiety as a substituent on the phenothiazine nitrogen atom. The effectiveness is particularly enhanced when the sulfur atom of the substituent group is in a beta position (i.e., 2-atoms removed) from the phenothiazine N-atom. Such compounds as later described herein have excellent anti-oxidant properties in lubricating oils.
Throughout the specification and claims, percentages and ratios are by weight, temperatures are degrees Celsius, and pressures are in Kpascals gauge unless otherwise indicated. References cited herein are incorporated by reference to the extent that they are applicable.